Feral pigeons (Columba livia domestica), also called city doves, city pigeons, or street pigeons, are derived from domestic pigeons that have returned to the wild.[2] The domestic pigeon was originally bred from the wild rock dove, which naturally inhabits sea-cliffs and mountains.[3] Rock (i.e., 'wild'), domestic, and feral pigeons are all the same species and will readily interbreed. Feral pigeons find the ledges of buildings to be a substitute for sea cliffs, have become adapted to urban life, and are abundant in towns and cities throughout much of the world.[4]

With domesticated populations, feral pigeons mate for life. Their courtship rituals can be observed in urban parks at any time of the year. The male on the ground or rooftops puffs up the feathers on the neck to appear larger and thereby impress or attract attention. He approaches the hen at a rapid walking pace while emitting repetitive quiet notes, often bowing and turning as he comes closer.

At first the female invariably walks or flies a short distance away and the male follows her until she stops. At this point he will continue the bowing motion and very often make full- or half-pirouettes in front of the female. The male will then proceed to feed the female by regurgitating food, as they do when feeding the young.

The male then mounts the female, rearing backwards to be able to join their cloacas. The mating is very brief with the male flapping his wings to maintain balance on top of the female.

Abandoned buildings are favorite nesting areas. Mass nesting is common as pigeons are a community flocking bird; often dozens of birds will share a building. Loose tiles and broken windows provide access, and pigeons are adept at spotting new access points, for example following property damage caused by strong winds.

Nests and droppings tend to stay clustered and remain dry when out of the weather. Pigeons are particularly fond of roof spaces. These often contain water tanks. Any water tank or cistern on a roof must therefore be secured and sealed off to keep the pigeons out of them. The popularity of a nesting area does not seem to be affected by the pigeons' population density.

Pigeon squab in nest

On undamaged property, the gutters, window air conditioners and empty air conditioner containers, chimney pots and external ledges are used as nesting sites. Many building owners try to limit roosting by using bird control spikes and netting to cover ledges and potential nesting places on buildings. This has little effect on the size of the pigeon population, but it can reduce the accumulation of droppings on and around a particular building location.

In the UK, only the larger and more wary common wood pigeon, which often shares the same territory and food supply, will build nests in trees, usually close to roads.

In Wendell Levi's The Pigeon, he describes the crowing/cooing of pigeons as mostly being associated with strutting and fighting in male birds.[3] Hens will also coo, but this is noticeably less guttural than the cooing of the cock. Cooing is also more frequent between couples during mating and nesting.

Pigeons breed when the food supply is abundant enough to support embryonic egg development, which in cities can be any time of the year. Laying of eggs can take place up to six times per year.

Pigeons mate for life, and are often found in pairs during the breeding season, but usually the pigeons are gregarious preferring to exist in flocks of from 50 to 500 birds (dependent on the food supply).[5]

Feral pigeons can be seen eating grass seeds and berries in parks and gardens in the spring, but there are plentiful sources throughout the year from scavenging (e.g., remnants left inside of dropped fast-food cartons) and they will also take insects and spiders. Additional food is also usually available from the disposing of stale bread in parks by restaurants and supermarkets and from tourists buying and distributing birdseed, etc. Pigeons tend to congregate in large, often thick flocks when feeding on discarded food, and have been observed flying skillfully around trees, buildings, telephone poles and cables, and even through moving traffic just to reach a food source.

In the UK Pigeons are covered under the 'General Licences' https://www.gov.uk/government/collections/bird-licences) and can be humanely culled by the land owner or their agent for a variety of reasons (mainly crop protection). It is not legal to kill/destroy nests for any other reason other than those listed under the general licences.

Feral pigeons often only have small populations within cities. For example, the breeding population of feral pigeons in Sheffield, England, has been estimated at only 12,130 individuals.[6] Despite this, feral pigeons usually reach their highest densities in the central portions of cities, so they are frequently encountered by people, which leads to conflict.

Large pigeon trap/coop/loft at Batman Park, Melbourne. Designed specifically to encourage nesting and allow removal of fertilised eggs to prevent population growth, it is a landmark in its own right.

One of the difficulties of controlling pigeon populations is the common practice of feeding them, as here in New York

Feral pigeons are often considered a pest or even vermin, owing to concerns that they spread disease[7] and are much maligned in the media for transmitting bird flu, but it has been shown pigeons do not carry the deadly H5N1 strain. It is rare that a pigeon will transmit a disease to humans due to their immune system. Three studies have been done since the late 1990s by the US Agriculture Department's Southeast Poultry Research Laboratory in Athens, Georgia, according to the center's director, David Swayne. The lab has been working on bird flu since the 1970s.

In one experiment, researchers squirted into pigeons' mouths liquid drops that contained the highly pathogenic H5N1 virus from a Hong Kong sample. The birds got 100 to 1,000 times the concentration that wild birds would encounter in nature. "We couldn't infect the pigeons," Swayne said. "So that's good news."[8][9]

There is ample reason for the concerns of pigeons damaging property, due to their size and proximity to people and their dwellings. Pigeons often cause significant pollution with their droppings, though there is little evidence of them driving out other bird species. Pigeons are labeled an invasive species in North America by the USDA.[10]

Long-term reduction of feral pigeon populations can be achieved by restricting food supply, which in turn involves legislation and litter (garbage) control. Some cities have deliberately established favorable nesting places for pigeons—nesting places that can easily be reached by city workers who regularly remove eggs, thereby limiting their reproductive success.[11] In addition, pigeon populations may be reduced by bird control systems that successfully reduce nesting sites.

Peregrine falcons, which are also originally cliff dwellers, have also adapted to the skyscrapers of large cities and often feeding exclusively on rock pigeons.[12] Some cities actively encourage this through falcon breeding programs. Projects include Unibase Falcon Project and the Victorian Peregrine Project.

Larger birds of prey occasionally take advantage of this population as well. In New York City, the abundance of pigeons (and other small animals) has created such a conducive environment for predators that the red-tailed hawk has begun to return in very small numbers, the most famous of which is Pale Male.

Due to their non-selective nature, most avian poisons have been banned. In the United States market only 4-aminopyridine (Avitrol) and DRC-1339 remained registered by EPA. DRC-1339 is limited to USDA use only while 4-AP is a restricted use pesticide, for use only by licensed applicators.

The use of poisons has been proven to be fairly ineffective, however, as pigeons can breed very quickly—up to six times a year—and their numbers are determined by how much food is available; that is, they breed more often when more food is provided to them.

When pigeons are poisoned, surviving birds do not leave the area. On the contrary, they are left with more food per bird than before. This attracts pigeons from outside areas as well as encouraging more breeding, and populations are re-established quickly.[15][not in citation given][page needed] An additional problem with poisoning is that it also kills pigeon predators. Due to this, in cities with peregrine falcon programs it is typically illegal to poison pigeons.[12]

A more effective tactic to reduce the number of feral pigeons is deprivation.[16] Cities around the world have discovered that not feeding their local birds results in a steady population decrease in only a few years. Pigeons, however, will still pick at garbage bags containing discarded food or at leftovers carelessly dropped on the ground. Feeding of pigeons is banned in parts of Venice, Italy.[17]

In 1998, in response to conservation groups and the public interest, the National Wildlife Research Center (NWRC), a USDA/APHIS laboratory in Fort Collins, Colorado, started work on nicarbazin, a promising compound for avian contraception. Originally developed for use in resident Canada geese, nicarbazin was introduced for use as a contraceptive for feral pigeons in 2007.

The active ingredient, nicarbazin, interferes with the viability of eggs by binding the ZP-3 sperm receptor site in the egg.[18] This unique contraceptive action is non-hormonal and fully reversible.[19]

Registered by the EPA as a pesticide (EPA Reg. No. 80224-1), "OvoControl P", brand of nicarbazin, is increasingly used in urban areas and industrial sites to control pigeon populations. Declared safe and humane, the new technology is environmentally benign[20] and does not represent a secondary toxicity hazard to raptors or scavengers.[21]

Dummy egg nesting programs have been tested in some cities with mixed results. Nest or coop structures are erected and the eggs are removed and replaced with dummy eggs. The real eggs are then destroyed. Such structures are being used in New York City[citation needed] and also the Melbourne city centre by the Melbourne City Council at Batman Park[22][22][23] The loft used in Melbourne is on stilts, with a cage door allowing access from beneath for accessing the structure at night when the pigeons are asleep.